Electric circuit breaker



Jan. 30, 1951 N. M. BEST ELECTRIC CIRCUIT BREAKER 4 Shgets-Sheet 1 Filed 001;. 5, 1945 7 Jan. 30, 1951 BEST 2,539,567

ELECTRIC CIRCUIT BREAKER Filed Oct. 5, 1945 4 Sheets-Sheet 2 fl/Mw 4 @M Jan. 30, 1951 N. M. BEST ELECTRIC CIRCUIT BREAKER 4 Sheets-Sheet 3 Filed Oct. 5, 1945 Jan. 30, 1951 N. M. BEST 2,539,567

ELECTRIC CIRCUIT BREAKER Filed Oct. 5, 1945 4 Sheets-Sheet 4 In 111/ 1/ III I I 1 [11L] I I//// III/ [I ,7

Patented Jan. 30, 1951 2,539,567 ELECTRIC CIRCUIT BREAKER Norman Maxwell Best, Hendon, London, England Application October 5, 1945, Serial No. 620,492 In Great Britain January 25,1944

Section 1, Public-Law 690,v August 8, 1946 Patent expires January 25, 1964.

Claims. 1

The present invention relates to a device for making and breaking electric. circuits; more particularly to a device of this kind which can. be operated manually to make and break the circuitand which ope ates automatically. as a result of an overload, to break the circuit to be protected.

One object of the invention is to provide an electric. switch which, on the occurrence of. a high overload such as a short circuit in the circuit to be protected, operates instantan'ously and automatically to break the circuit and which on the occurrence of a lower and. perhaps. gradual overload, operates automatically after. a short period of time to open the circuit.

According to this invention there is provided an electric switch comprising a base, frame mounted on the base and formed with a slot, a handle pivoted on the frame and formed with a cam surface, an. arm in contact with the cam surface, a pivot on one end of the arm. and acontact on the other end, the pivot being movable within limits in the slot, a spring, bearing directly and permanently against the arm at a. point intermediat the contact and the pivot and. serving to urge the arm to the switch-open position, a. trigger removably engaging the pivot on the arm and means for operating the trigger when the current through the switch exceeds a. predetermined value, the arrangement being such that when the handle is manually moved to the switch-closed position, the cam surface cams the arm to the closed position against the action of the spring and when the current through the switch exceeds a predetermined value, the trigger releases the pivot and the spring rotates the arm to the switch-open posi tion, the handle meanwhile being rotated by the arm to the switch-open position. In order that the. nature of the invention may be clearly appreciated preferred embodiments. will now be described with reference to the accompanying diagrammatic drawings in which,

Figure 1 is a circuit diagram showing the internal connections of a switch according to the invention,

Figure 2 is an elevation of a switch, a front supporting bracket of which is. removed to show the parts of the device in their open positions, Figure 3 is an elevation of the switch, the front supporting bracket of which is broken away to show some of the parts in their closed positions,

Figure 4 is an elevation showing the parts, after release on overload, in aposition intermediate-of the open and closed positions,

Figure 5 is an end view of the device but with its. operating handle removed.

Figure 6 is a side. elevation of a modified form of switch constructed. in accordance with the present invention,

Figure '7 is an. end elevation of the same device, whilst Figures 8 and 9 are side elevations ofv further modified forms of switches constructed in ac cordance with the invention.

The circuit breaker illustrated in Figures 1-5 comprises an insulating base it on which are mounted fixed terminals l l and i la and a moving, contact arm l2 carrying a contact [3. Current from the circuit-to be protected entersthe switch through the fixed terminal I l and, when contacts ll-l3 are closed, as shown in Figure 3, passes. from the arm l2 to the windings of an electro-magnet l4 thence through a bimetallic strip l5 and. from the strip passes again to the circuit to be protected through terminal Ha. An armature IE of the electro-magnet is held by screws I! the shanks of which pass freely through holes in a two-armed release trigger [8, compression springs 19 being inserted between the trigger IB and the armature Hi. The two-armed trigger l-B is pivoted at 2B and is normally urged in anti-clockwise directionv by a trigger r'turn spring 2!. The lower arm of the trigger [8 is formed with a notch 22 which in. the position illustrated serves to hold a floating pivot 23 for the arm [2 at the top of slots 24 formed in the supporting brackets 25 of. the switch frame.

Contacts Hl3" c'an be closed by means of a. manually operable handle 26 pivoted in the frame at 2'! and formedv with a cam surface 58, which. handle when moved to. its right-hand or switch-open position against a stop 59 cams the floating, arm 12 downwardly against the action of a strong compr ssion. spring 28 and reaches an. overset position in which the. contacts are retained closed. Reverse movement of the handle opens the contacts.

The pivot 23' can be released from the notch 22 by rotation of the release trigger is in clock-- wise direction and this can be effected either by suitable energi'sation of the electro magnet I4 in such manner that the magnet 29 thereof pulls the armature l5 downwardly, or by anticlockwise rotation of a T-shaped lever 30 pivoted at 31 in such manner that the stem 32 of the T pushes the two-armed lever in clockwise rotation. Normally the T-shaped lever to is latched against rotation by the lower end of the bimetallic strip P51 The handle needs no stop at the switch-open position, the flat on this side of the handle serving to arrest its motion at the appropriate position.

The operation of the device is as follows: When the handle 25 is moved to the right, i. e. to the switch closed position, its cam surface 58 forces the arm I2 downwards against the action of the spring 28 thus closing the contacts II-l3 and allowing current to flow. Current of normal strength passes in series from terminal ll to contact 13 through arm I2 to the windings of electro-magnet I 4 thence through the bimetallic strip [5 and out to the circuit to be protected through terminal Ha. Current of normal strength passing through the windings M is insufficient to attract the armature 16 with strength enough. to move it against the restraini g action of the trigger return springs 21.

If, however, a sudden high overload occurs, the armature I6 is attracted towards the magnet 29 and assoon as pivot 23 begins to ride over the point of the notch 22 the compression spring 28 using the cam surface 58 as a fulcrum serves to assist this motion and the pivot 23 is released in its slots 24 (Figure 4). The compression spring 23 then moves the arm l2 into the horizontal or open position with the pivot 23 in its original position as shown in Figure 2 and this movement of the arm l2 serves to rotate the handle 26 into the switch-open position as also shown in Figure 2. The contacts lle| 3 are thus opened and the circuit to be protected broken. As current hasno-w ceased to flow in the coil M the armature and release trigger 18 return under the influence of the trigger return springs 2! to their original positions.

The device is now completely reset and movement of the handle 26 to the switch-close position will re-connect the circuit unless the shortcircuit conditions still obtain. In that event con tact is made momentarily but the armature i6 is instantaneously moved downwardly and the same sequence of operations occurs to break the circuit.

If an overload of less magnitude is imposed on the circuit to be protected, forv example if the current slightl increases over the safe load, the current passing through the windings of the electro-magnet I i is insuflicient to move the armature it but the bimetallic strip {5 is heated sufliciently to cause its lower end to move away from the T-shaped lever 30. When this happens the compression spring 28 rotates the lever 31] in anti-clockwise direction, thus rotating the release trigger is in clockwise direction so that the pivot 23 is again disengaged from the notch 22,- whereupon the arm I2 rotates in clockwise direction into the switch-open position shown in Figure 2. After the braking operation has been completed the T-shaped lever 30 is returned to its normal position by means of a return spring 33 which is positioned underneath it and which is sufiiciently powerful to overcome the force of the compression spring when this latter is uncompressed. Y

Although the device is now. reset the contacts 4 cannot be closed until the bimetallic strip [5 has cooled and therefore straightened to allow the release trigger I8 to be in its normal position. The time interval while the strip [5 is cooling is sufiicient to allow the apparatus which is connected in the external circuit and which has been over-heated by the excess current to cool before re-connection.

When the circuit to be protected is clear of its overload the switch may be reset by simple movement of the handle 26 which, it will be appreciated, is a much simpler operation than the rewiring of the well-known fuse-box.

The fact that the clockwise rotation of the trigger I8 is completed by the action of the spring 28, although initiated on the movement of the armature l6 afiords the advantag that the latter can be set very close to the magnet of the electro-magnct Hi thus enabling an electromagnet of small power to be used.

It will be seen that the supporting brackets 25 of the frame constitute parts of the north and south poles of the electro-magnet and that they etxend on either side of the make and break contacts H and it. With this arrangement there is achieved an electro-Inagnetic blow out of the are formed between the contacts ii and I3.

In Figures 6 and 7 are illustrated an embodiment of the invention which differ from the last described example in that the electro-magnetic switch is arranged so that its armature or core moves horizontally and both the armature and the bimetallic strip operate positively on a trigger arm of the switch.

Clockwise rotationof a handle 35 causes a moving contact arm 36 to close the electric circuit b rocking in an anti-clockwise direction about a pivot 31 carried in slots 38 in the supporting bracket 39, movement being against the action of a spring 49 which is in the form of a Phosphor bronze strip. Current passes from the terminal 45!, via a Phosphor bronzestrip 43 to a lower contact id, thence to the contact 42, thence along the PhOSphOr bronze strip to one end 45A of the electro-magnetic coil 65 which is of larger size than that used in the previous embodiment of the invention. The strip 43 serves as conductor and as a spring to allow the lower contact some vertical movement to compensate for contact wear etc. When the contacts 42 and 44 are closed the lower one 44 moves slightly downwards which movement also causes a rubbing and sliding action between the two contacts thereby helping to keep them clean. A U-section trigger arm 56, pivoted at 47 and normally,

urged in a clockwise direction by a spring 48, is connected by a link is to one end of a horizontally movable core 50 of the electro-magnetic coil 45, the other end of the core 56 receiving a screw 5!, the shank of which passes freely through an aperture in a bimetallic strip 52. One end of this strip 52 is connected at 53 with one end of the coil Q5 and the other end of the strip is connected with the terminal 3! A of the switch. The electric circuit is identical with that shown in Figure 1. 2

As will be seen from Figures 6 and 7 the underside of the base 54 of the switch is recessed to receive the wiring, terminals etc., whilst the spring 46 passes through a slot 555 in the base 56 to the coil it.

When a high overload occurs in the circuit in which the switch is connected the increase in the. strength of the magnetic field of the. coil d5 causes its core 53 to bedrawn further, into the coil, i. e. to the right in Figure 6, and the trigger arm 48 is therefore rocked in an anticlockwise direction about its pivot 41 so that the pivot 37 of the arm 36 begins to ride over the point of the notch 55 on the trigger arm 45. This motion is assisted by the compression of the Phosphor bronze spring 40 and the pivot 31 is first released so as to be free to move in the slots 38 in the supporting bracket 39 after which the arm 36 is moved into the open position shown in Figure 6 so that the electric circuit is broken with a snap action due to spring 40. Movement of the contact arm 36 also causes the handle 35 to return to its off position whilst the trigger arm 46 is returned to its inoperative position under the action of the spring 48.

Should the circuit be subjected to an overload of less magnitude undue heating of the circuit causes the bimetallic strip 52 to bend to the right in Figure 6 and at a predetermined temperature the screw 5|, and with it the core 50, are forced in the same direction so that the trigger arm 46 is again released and the contacts opened with a snap action as before.

In Figures 8 and 9 are illustrated embodiments of the invention in each of which the circuit is broken at only one predetermined current value, like parts being designated by like reference numerals.

In the arrangement illustrated in Figure 8, the trigger arm 46 is connected by a screw 51 to the bimetallic strip 52, the only difference between this arrangement and that shown in Figures 6 and 7 being that an electromagnet is not included.

Figure 9 illustrates an embodiment in which the circuit breaker is operated by movement of the core 50 of the electro-magnetic coil 45, there being no bimetallic strip in this arrangement.

The percentage overloads at which either instantaneous or delayed operation takes place can be regulated in manufacture by variation of the strength of the electro-magnet or the dimensions of the bimetallic strip to suit the requirements of the circuit to be protected. The time interval between commencement of overload and operation of breaker will be approximately inversely proportional to the degree of overload.

The breaking of the circuit under overload conditions is independent of the operating handle and the circuit will be broken even if the handle is held continuously in the on position.

The circuit will be made and then broken again instantaneously if the handle be moved to the on position when conditions in the circuit are such that an overload current will flow when the circuit is completed. In other words the handle is trip-free.

It will be seen also that, by means of this invention, there is provided, for an electric circuit, a switch and the equivalent of a fuse combined in a single housing and mounted as a, unitary structure.

I claim:

1. An electric switch comprising a base, a frame mounted on the base and formed with a slot, a

handle pivoted on the frame and formed with a cam surface, an arm in contact with the cam surface, a pivot on one end of the arm and a contact on the other end, the pivot being movable within limits in the slot, a spring bearing directly and permanently against the arm at a point intermediate the contact and the pivot and serving to urge the arm to the switch-open position, a trigger removably engaging the pivot on the arm and means for operating the trigger When the current through the switch exceeds a predetermined value, the arrangement being such that when the handle is manually moved to the switchclosed position, the cam surface cams the arm to the closed position against the action of the spring and when the current through the switch exceeds a predetermined value, the trigger releases the pivot and the spring rotates the arm to the switch-open position, the handle meanwhile being rotated by the arm to the switchopen position.

2. An electric switch as claimed in claim 1, including an electromagnet for operating the trigger when the current through the switch exceeds the predetermined value suddenly.

3. An electric switch as claimed in claim 1, including an electromagnet for operating the trigger when the current through the switch exceeds the predetermined value suddenly, and a bi-metallic strip for operating the trigger when the current through the switch creeps slowly above the predetermined value.

4. An electric switch as claimed in claim 1, including an electromagnet, the armature of which is coupled to the said trigger and a bi-metallic strip loosely linked with the armature, the arrangement being such that when the current through the switch exceeds the predetermined value suddenly, the armature is moved to operate the trigger and when the current through the switch creeps slowly above the predetermined REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,154,237 Frank Apr. 11, 1939 2,184,372 Von Hoorn Dec. 26, 1939 2,233,187 Von Hoorn Feb. 25, 1941 2,270,150 Taylor Jan. 13, 1942 2,300,884 Gano Nov. 3, 1942 2,357,151 Von Hoorn Aug. 29, 1944 

